Negotiating a transmit wake time

ABSTRACT

Includes receiving, from a link partner, a message specifying a link partner receive wake time and resolving to a transmit wake time.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/236,463, filed on Aug. 14, 2016, entitled “NEGOTIATING A TRANSMITWAKE TIME”, which is a continuation of U.S. patent application Ser. No.14/504,654, filed on Oct. 2, 2014, now U.S. Pat. No. 9,454,204, andentitled “NEGOTIATING A TRANSMIT WAKE TIME”, which is a continuation ofU.S. patent application Ser. No. 13/489,434, filed on Jun. 5, 2012, nowU.S. Pat. No. 8,898,497, and entitled “NEGOTIATING A TRANSMIT WAKETIME”, which is a continuation of U.S. patent application Ser. No.12/381,811 filed on Mar. 17, 2009, now U.S. Pat. No. 8,201,005, andentitled, “NEGOTIATING A TRANSMIT WAKE TIME”. The current applicationclaims priority to the U.S. Ser. No. 12/381,811 application via the U.S.Ser. Nos. 13/489,434, 14/504,654 and 15/236,463 applications.applications Ser. Nos. 12/381,811, 13/489,434, 14/504,654 and 15/236,463are incorporated by reference in their entirety herein.

BACKGROUND

Many modern computer systems try to opportunistically reduce powerconsumption during periods of reduced activity. Common techniquesinclude reducing or shutting down voltage power supply levels to one ormore system components, stopping clocks, and so forth.

Different power consumption modes for computer systems have been dubbedC_(n) (or alternately S_(n) or P_(n)) states which indicateprogressively greater power savings modes. The different modes oftenfeature different wake latencies—the amount of time needed to resume ahigher power mode. Thus, the choice of entering a particular powersaving mode often requires a balancing between the amount of powersavings and the amount of time needed to wake.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a timeline of transmissions by a link partner.

FIG. 2 is a diagram illustrating resolution of transmit wake times bylink partners.

FIG. 3 is a flow-chart of a process to determine a transmit wake time.

FIG. 4 is a flow-chart of a process to enable a link partner to powerdown.

FIG. 5 is a flow-chart of a process to resume data transmission to alink partner.

FIG. 6 is a diagram illustrating link partners.

FIG. 7 is a diagram of a network interface controller.

FIGS. 8, 9, and 10 are diagrams of auto-negotiation messages.

FIGS. 11, 12, and 13 are diagrams of link layer discovery protocolframes.

DETAILED DESCRIPTION

In networking systems, a link connects and permits communication betweentwo link partners. Data transmission between link partners can vary fromlarge bursts of data to periods where no data needs to be transmitted atall. The absence of data transmission permits components in both linkpartners to enter low power modes. For example, the transmit circuitryin one link partner and the receive circuitry in the other link partnercan both enter a low power mode. A low power mode may apply only tonetworking components. For example, the low power mode may strictlyapply to a PHY, a component that handles physical transmission of datasignals over a link. However, a low power mode may also potentiallyextend to other system components. For instance, when a serveranticipates a lower volume of network traffic, the server can power downone or more processor cores and other system components (e.g., spinningdown disks and so forth). As described above, a longer sleep durationcan permit a system to enter a deeper power saving mode, though often atthe expense of an increased wake latency. Thus, the larger the amount oftime a system is given to wake, the more power that can be saved.

As described below, to potentially increase the continuous “quiet”duration available and thus enable the system to enter into a deeperpower saving mode, a link partner can “borrow” time from its remote linkpartner by requesting a guarantee that the remote partner wait an amountof time (Tw system) after initially sending wake symbols to begin datatransmission. For example, a transmitting link partner can buffer datain a transmit buffer to delay transmitting data to a link partner whilethe link partner wakes. The transmitting link partner may also use otherways to delay transmission, for example, by sending flow controlmessages to upstream nodes. The receive partner can use this known delayto enter a deeper power saving state that requires a longer wake-timeand possibly postpone wake-up operations without suffering loss of databetween the link partners. The amount of time a transmitter commits toproviding to a receiver is a Tw system (a system transmit wake) valuenegotiated by the transmitter and receiver. A receiver can potentiallyadd the Tw system time of its link partner to time provided, forexample, by its own receive buffers, permitting an even larger timewindow to wake to further reduce system power consumption.

In greater detail, FIG. 1 depicts operation of a transmitting linkpartner over time. As shown, the link partner is initially active 100,transmitting data or idle symbols. When a temporary halt in transmissionis foreseen (e.g., a transmit buffer is empty or falls below somethreshold or the transmitting node itself is not receiving data), thetransmitting link partner sends sleep symbols to its partner for aduration Ts 102. The transmitting link partner can then enter a reducedpower mode 112. During this time, quiet periods (Tq 104 a-104 b) areperiodically interrupted by brief refresh periods, Tr, 106 a-106 b wherethe link partners perform timing recovery and coefficientsynchronization.

After determining transmission is to resume, the transmitting linkpartner wakes its PHY to an active mode. This takes an amount of time TwPHY 108. Even after Tw PHY 108, however, the transmitting link partnercontinues to delay transmission of data until time Tw system 110 haselapsed, giving the receiver an additional Tw system 110 amount of timeto wake beyond the initial transmission of wake symbols.

The Tw system 110 value may be derived in a variety of ways. Forexample, a receiver may request a desired amount of time, Tw Rx, beforedata transmissions resume. The receiver may determine the value of Tw Rxbased on a variety of factors such as system performance requirements,system wake time, the size of a receive buffer to store data, the timeneeded to wake the receiver PHY, and/or on the power saving mode sought.

A transmitter may likewise determine an amount of time, Tw Tx , that thetransmitter offers to delay data transmission after transmission of wakesymbols. Again, the Tw Tx value may be based on a variety of factorssuch as the Tw PHY value of the transmitter and/or the amount of atransmit buffer available to the link.

The Tw system value, the negotiated amount of time a transmitter commitsto delaying transmission, can be resolved to the lesser of thetransmitters Tw Tx value and the receivers Tw Rx value. This ensuresthat both link partners can support the negotiated Tw system value.

Typically, a link supports a duplex connection between partners. Thatis, both partners send and receive data. Thus, the different directionsof a link may be characterized by different Tw system values and eachpartner may have its own Tw Tx and Tw Rx values. The negotiation of theTw system values may feature an exchange of the Tw Tx and Tw Rx valuesbetween the partners.

FIG. 2 illustrates a sample negotiation between link partners LP1 andLP2. As shown, link partner LP1 has a Tw Rx_((LP1)) value of 20 ms and aTw Tx_((LP1)) value of 10 ms. In other words, link partner LP1 isrequesting a delay of transmission from partner 204 of 20 ms and offersa 10 ms delay of transmission to partner LP2. Similarly, link partnerLP2 has a Tw Tx_((LP2)) value of 15 ms and a Tw Rx_((LP2)) value of 5ms.

After exchange of these values between partners, both partners candetermine the Tw system_((LP1)) and Tw system_((LP2)) values. In theexample shown, the exchanged values yield a Tw system_((LP1)) value of 5ms for transmission from partner LP1 to partner LP2. In other words,while partner LP1 offered a 10 ms delay, LP2 only requested a 5 msdelay. Likewise, the Tw system_((LP2)) value resolves to a Twsystem_((LP2)) value of 15 ms—the lesser of the 20 ms delay requested bypartner LP1 and the 15 ms delay offered by partner LP2.

While FIG. 2 illustrates a single negotiation, the negotiation may beperformed any number of times based on system performance or energysavings priorities. For example, partner LP2, after having received TwTx_((LP1)) may determine a deeper sleep mode may be possible andinitiate a renegotiation with a larger Tw Rx_((LP2)) value.Additionally, the Tw Rx and Tw Tx values of a link partner may changeover time. For example, as fewer buffers may be allocated to aparticular link, a partner may offer a smaller Tw Tx value. Likewise, apartner may determine a deeper power reduction mode is not possible dueto other network traffic or system load and reduce its request (e.g., asmaller Tw Rx value). Additionally, the possible values of Tw system maybe bounded by defined Tw system min and max values. Typically Tw minwould be determined by the resume capabilities of the physical layertransceiver (PHY) being used.

FIG. 3 depicts a sample negotiation flow 300 of a local link partner. Asshown, after determining local Tw Tx and Tw Rx values 302, these valuesare transmitted to a remote link partner 304. Before or after thistransmission, the Tw Tx and Tw Rx values of the remote link partner arereceived 306. The egress Tw system value of the link partner is resolved308 to the lower of the local Tw Tx value and the remote Tw Rx value. Inthe absence of an exchange of the Tw values, the Tw system value maydefault to a specified Tw min value.

FIGS. 4 and 5 depict sample operation 400 after the negotiation. Asshown in FIG. 4, when LP1 determines 402 transmissions to LP2 may betemporarily suspended, LP1 sends sleep symbols 404 to LP2. Thereafter,LP1 powers down 406 its transmission circuitry. When LP2 receives thesleep symbols 408, LP2 also enters a lower power state, for example, bypowering down receive circuitry 410.

As shown in FIG. 5, when LP1 determines 502 transmission to LP2 willshortly resume, LP1 sends 504 wake symbols to LP2. After receipt 506,LP2 wakes 508, for example, fully powering the LP2 PHY receivecircuitry. LP1 delays data transfer to LP2 (e.g., buffers Tx data) afterinitial transmission of the wake symbols for, at least, the negotiatedTw system time period for the egress link of LP1. Thereafter, LP1transfers the data buffered during the Tw system period and operationreturns to normal.

The techniques described above may also be used when a link has a lowbandwidth utilization rate compared to the maximum data throughputcapabilities of the link. For example, when data destined for LP2 isarriving at a very slow rate with respect to the size of the transmitterTx buffer, LP1 can send sleep symbols and enable LP2 to enter a lowpower mode while the Tx buffer of LP1 slowly accumulates data. Whenstored data in LP1's Tx buffer exceeds some watermark threshold thatstill permits an egress Tw system transmission delay, LP1 can send wakesymbols.

FIG. 6 illustrates sample architecture of link partners LP1 602 and LP2612. In this example, LP1 is a host computer system having a one or moreprocessors 606. For example, the processors may be programmable coresintegrated on the same die or within the same package. The system 602includes a network interface controller (NIC) 610. The NIC 610 may be anintegral part of the system (e.g., integrated within a motherboard orthe same die as the processor(s)) or an attached unit (e.g., a NICcard).

Also shown in FIG. 6 is a power management unit 608. The powermanagement unit 608 includes circuitry to control power usage by systemcomponents. For example, the power management unit 608 may initiate oneof several different sets of varying power usage modes (e.g., Cn, Sn, orPn sleep modes) where increasing values of n correspond to deeper powersaving modes. The power management unit 608 may also control powerprovided to other components (e.g., processor, chipset, accelerators,I/O systems, mass storage devices, and so forth). For example, the powermanagement unit 608 may interact with the NIC 610 and/or NIC PHY 620 tocontrol power usage. For example, the power management unit 608 mayaccess Tw PHY data from the PHY (e.g., stored in a PHY registeraccessible to external components) to determine a local Tw Rx value. Thepower management unit 608 may also sent data to the PHY 620 indicating adesired Tx Rx based on the amount of wake time needed for a particularpower saving mode selected from a set of power saving modes (e.g., C_(n)or P_(n)).

The power management unit 608 may implement different policies todetermine a target power saving mode/Tx Rx. For example, a powermanagement unit 608 for a battery powered mobile system or laptop mayattempt to negotiate sufficient time to enter a more aggressive powersavings mode than a continually powered desktop system. The powermanagement unit 608 may also take into account thermal considerations.For example, an extended power saving period permits a greater amount ofthermal dissipation which may be particularly advantageous in compactmobile devices. In the event negotiation of a Tw system value does notpermit entry into a desired power saving mode, the power management unitcan select a power saving mode that requires a smaller wake latency andattempt renegotiation with a smaller Tw Rx value.

The power management unit 608 may initiate power savings based, at leastin part, on the negotiated ingress Tw system value. The power managementunit 608 may also select a power saving mode based on other factors suchas requirements of executing applications, the systems receive buffersize, and so forth. After receiving sleep messages, the power managementunit 608 may be notified of the current Tw system value. Alternately,the value may have been communicated previously (e.g., whenevernegotiated) and the power management unit 608 is informed only of thearrival of sleep messages. Thereafter, the power management unit 608 caninitiate entry into a selected power mode, again, based at least inpart, on the ingress Tw system value (e.g., a higher Tw system valueresults in a deeper power saving mode). After the power management unit608 is notified of receipt of wake messages, the power management unit608 can initiate waking of system components to enter a differentselected power mode.

As shown, LP1 602 shares a link with switch LP2 612. The link may be acabled, electrical backplane, wireless, or optical link, in turn,requiring the appropriate physical transceiver (PHY) circuitry.

The switch 612 connects to the link via PHY 622. As shown, the switch612 features packet processing circuitry 616 such as an ASIC(Application Specific Integrated Circuitry) or Network Processor toperform switching operations such as forwarding lookups, etc. The switch612 may also feature a power management unit 618 that operates asdescribed above, for example, by interacting with the PHY 622 to accessTw PHY and determine Tw Tx or set Tw Rx based on switch 612 wakelatencies. The power management unit 618 may also coordinate powerconsumption of switch 612 components based, at least in part, on anegotiated ingress Tw system value. For example, the power managementunit 618 may enter different power modes based on receipt of sleep orwake symbols from LP1 602.

Though FIG. 6 illustrated link partners as a host computer system 602and a switch 612, the operations described above may be implemented byother devices. For example, the link partners may be blades or linecards interconnected by a backplane. Additionally, though LP1 and LP2are depicted as featuring a single link, either system may featuremultiple links and negotiate respective Tw system values for each asdescribed above. Further, while FIG. 6 depicts a discrete powermanagement unit 608, the power management operations described above maybe implemented in other circuitry.

FIG. 7 illustrates a sample NIC 700 in greater detail. As shown, the NIC700 features a PHY 706 to perform physical signaling, a media accesscontroller (MAC) 704, for example, to perform framing operations, and adirect memory access (DMA) engine to transfer packets between hostmemory and the NIC 700. The MAC 704 and PHY communicate via an egress Txqueue and ingress Rx queue in memory 708. The PHY 706 may feature one ormore externally accessible registers to store Tx PHY and/or Tx Rxvalues.

Circuitry to perform the Tw system negotiation described above may belocated in a variety of places within NIC 700. For example, thenegotiation may be performed by physical coding sublayer (PCS) circuitrywithin the PHY 706. Alternately, the circuitry may be located within MAC704. In other implementations, the circuitry may be implemented outsideof the NIC 700, for example, in a power management unit or by driversoftware executed by a processor.

NIC architectures vary considerably from the one illustrated in FIG. 7.For example, some feature multiple instances of one or more of thecomponents (e.g., multiple DMA engines, or multiple MACs and PHYs).Additionally, other NIC architectures feature offload circuitry (e.g., aTCP/IP [Transmission Control Protocol/Internet Protocol] offload engineor a CRC [Cyclic Redundancy Check] engine).

FIGS. 8-13 are diagrams of messages of messages that can be used toperform operations described above. More specifically, FIGS. 8-10 depictinitial Ethernet PHY autonegotiation while FIGS. 11-13 depict LLDP (LinkLayer Discovery Protocol) messages that can be used to exchange Twvalues.

In greater detail, during initial auto-negotiation, a PHY can transmit aFast Link Pulse identifying its capabilities. A fast link pulse mayinclude, for example, 33-time slots with even slots carrying messagedata pulses. Each set of pulses is known as a page. As shown in FIG. 8after an initial page carrying a technology ability field (TAF), asubsequent page may include a value of 0×0A to identify Energy EfficientEthernet (EEE) capabilities. FIG. 9 depicts a subsequent page thatidentifies whether EEE is supported for different technologies. Afurther page, shown in FIG. 10, can identify a ratio between a PHYs Tqand Tr. The higher the ratio, the greater the opportunity for energysavings. For example, a “reduced energy” refresh duty cycle value (e.g.,0) may feature a Tq:Tr ratio of n:1 while a “lowest energy” refreshvalue (e.g., 1) may feature a greater Tq;Tr ratio. The link PHYs canadvertise the refresh duty cycle values and resolve to the lower of thevalues.

As shown in FIG. 11, link layer discovery protocol (LLDP) messages maybe used to exchange data between link partners. Briefly, LLDP (e.g.,IEEE (Institute of Electrical and Electronic Engineers) 802.1AB) definesa set of type-length-value (TLV) fields used to identify the values ofdifferent types of data. As shown, in addition to fields required byLLDP, an LLDP message can include System Wake Times and EEE PHYparameters. As shown in FIG. 12, the system wake timers can include theTw Tx and Tw Rx values for a link partner. That is, each link partnermay send an LLDP message as shown in FIGS. 11 and 12 to exchange Twvalues. As shown in FIG. 13, the EEE PHY parameters can include therefresh cycle value instead of, or in addition to, being communicated inthe autonegotiation process.

The message formats shown in FIG. 8-13 are merely examples. For example,the data may be stored in different fast link pulse time slots or indifferent LLDP fields. Additionally, a wide variety of other techniquesfor communicating the Tw and/or PHY values may be used. For example,instead of, or in addition to, LLDP messages, Tw and PHY values may beexchanged via MCF (Mac Control Frames). Additionally, other informationmay be exchanged. For example, link partners may exchange their Tw PHYvalues as part of the negotiation to provide greater information to alink partner. This can facilitate a renegotiation based on the Tw PHYvalue (e.g., a system cannot offer a Tw system value less than Tw PHY).

The term circuitry as used herein includes hardwired circuitry, digitalcircuitry, analog circuitry, programmable circuitry, and so forth. Theprogrammable circuitry may operate on computer program instructionsstored on tangible computer readable storage mediums.

Other embodiments are within the scope of the following claims.

What is claimed is:
 1. A method, comprising: receiving, from a linkpartner, a message specifying a receive wake time for the link partner;resolving to a transmit wake time based on the receive wake time for thelink partner and a local transmit wake time; receiving a request totransmit data to the link partner; and after sending a wake signal tothe link partner, waiting for at least the transmit wake time to delaytransmitting data to the link partner.
 2. The method of claim 1, furthercomprising: determining the local transmit wake time based on transmitbuffer space available for transmitting data to the link partner; andwherein waiting for at least the transmit wake time to delaytransmitting data to the link partner includes buffering data destinedfor the link partner.
 3. The method of claim 2, receiving the message,resolving to the transmit wake time, and buffering data comprisesreceiving, resolving, and buffering at a switch.
 4. The method of claim1, comprising resolving to a longer transmit wake time based on a lowbandwidth utilization rate to transmit data to the link partner comparedto data throughput capabilities.
 5. The method of claim 1, the messagefurther specifies a link partner transmit wake time; and determining alocal receive wake time based, at least in part, on a wake time of alocal physical layer.
 6. The method of claim 5, determining the localreceive wake time further comprises determining based on separate wakerequirements of at least two power reduction modes.
 7. The method ofclaim 6, comprising the separate wake requirements based on a networktraffic load through the local physical layer.
 8. The method of claim 7,comprising the network traffic load to cause a deeper power reductionmode to be excluded from the at least two power reduction modes.
 9. Themethod of claim 6, comprising the separate wake requirements based onthermal characteristics of a system that includes the local physicallayer.
 10. The method of claim 5, wherein the local physical layercomprises a PHY.
 11. The method of claim 1, comprising: transmitting aframe to the link partner, the frame including the local transmit waketime and a local receive wake time.
 12. The method of claim 1, themessage comprises a link layer discovery protocol frame.
 13. The methodof claim 1, comprising: periodically receiving, from the link partner,refresh signals during a low power mode of the link partner; andperforming timing recovery and coefficient updating responsive to eachreceived refresh signal.
 14. A system, comprising: a media accesscontroller; and circuitry to: receive, from a link partner, a messagespecifying a receive wake time for the link partner; resolve to atransmit wake time based on the receive wake time for the link partnerand a local transmit wake time; receive a request to transmit data tothe link partner; send a wake signal to the link partner; and wait forat least the transmit wake time to cause a delay to transmission of datato the link partner.
 15. The system of claim 14, further comprising: atransmit buffer; and the circuitry to determine the local transmit waketime based on transmit buffer space available in the transmit buffer,wherein to wait for at least the transmit wake time to cause a delay totransmission of data to the link partner includes causing data destinedfor the link partner to be buffered in the transmit buffer.
 16. Thesystem of claim 14, further comprising: a local physical layer; and thecircuitry to store a transmit wake value for the local physical layerthat indicates the local transmit wake time.
 17. The system of claim 16,comprising: the message to further indicate a link partner transmit waketime; and the circuitry to determine a local receive wake time based, atleast in part, on the transmit wake value for the local physical layer.18. The system of claim 17, comprising: the circuitry to determine thelocal receive wake time based on separate wake requirements of at leasttwo power reduction modes.
 19. The system of claim 18, comprising theseparate wake requirements based on a network traffic load through thelocal physical layer.
 20. The system of claim 19, comprising the networktraffic load to cause a deeper power reduction mode to be excluded fromthe at least two power reduction modes.
 21. The system of claim 18,comprising the separate wake requirements based on thermalcharacteristics of the system.
 22. The system of claim 14, comprisingthe circuitry to resolve to a longer transmit wake time based on a lowbandwidth utilization rate to transmit data to the link partner comparedto data throughput capabilities.
 23. The system of claim 14, furthercomprising the circuitry to cause a message to be transmitted to thelink partner, the message to include the local transmit wake time andthe receive wake time.
 24. The system of claim 14, the message comprisesa link layer discovery protocol frame.
 25. The system of claim 14,further comprising the circuitry to: periodically receive, from the linkpartner, refresh signals during a low power mode of the link partner;and perform timing recovery and coefficient updating responsive to eachreceived refresh signal.
 26. The system of claim 14, further comprising:memory; a processor; and a power management unit, the power managementunit to indicate to the circuitry a wake period associated with aselected one of multiple power reduction modes.
 27. The system of claim26, the power management unit enters a selected one of multiple powerreduction modes based on the transmit wake time.
 28. The system of claim14 comprises an Ethernet switch.
 29. A method, comprising: receiving,from a link partner, a message specifying a transmit wake time for thelink partner; resolving to a transmit wake time based on the transmitwake time for the link partner and a local receive wake time; afterreceiving a sleep message from the link partner, entering a system powersaving mode based, at least in part, on the resolved transmit wake time;after receiving a wake signal from the link partner, exiting the systempower saving mode; and receiving data from the link partner no soonerthan the resolved transmit wake time.
 30. The method of claim 29,further comprising: notifying a system power management unit of theresolved transmit wake time.
 31. The method of claim 30, notifying thesystem power management unit comprises notifying after receiving thesleep message.
 32. The method of claim 29, further comprising:periodically receiving, from the link partner, refresh signals while inthe system power saving mode; and performing timing recovery andcoefficient updating responsive to each received refresh signal.
 33. Themethod of claim 29, further comprising determining the local receivewake time based on a wake time of a local physical layer.
 34. The methodof claim 33, determining the local receive wake time further comprisesdetermining based on separate wake requirements of at least two powerreduction modes
 35. The method of claim 34, comprising the separate wakerequirements based on a network traffic load through the local physicallayer.
 36. The method of claim 35, comprising the network traffic loadto cause a deeper power reduction mode to be excluded from the at leasttwo power reduction modes.
 37. The method of claim 34, comprising theseparate wake requirements based on thermal characteristics of a systemthat includes the local physical layer.
 38. A switch, comprising: firstcircuitry to forward lookups; and second circuitry to: receive, from alink partner, a message specifying a receive wake time for the linkpartner; resolve to a transmit wake time based on the receive wake timefor the link partner and a local transmit wake time; receive a requestto transmit data to the link partner; send a wake signal to the linkpartner; and wait for at least the transmit wake time to cause a delayto transmission of data to the link partner.
 39. The switch of claim 38,further comprising: a power management unit, the power management unitto indicate to the second circuitry a wake period associated with aselected one of multiple power reduction modes.
 40. The switch of claim39, the power management unit enters a selected one of multiple powerreduction modes based on the transmit wake time.
 41. The switch of claim38, further comprising: a transmit buffer; and the second circuitry todetermine the local transmit wake time based on transmit buffer spaceavailable in the transmit buffer, wherein to wait for at least thetransmit wake time to cause a delay to transmission of data to the linkpartner includes the second circuitry to cause data destined for thelink partner to be buffered in the transmit buffer.
 42. The switch ofclaim 38, further comprising: a local physical layer, the secondcircuitry included in the local physical layer; and the second circuitryto store a transmit wake value for the local physical layer thatindicates the local transmit wake time.
 43. The switch of claim 42,comprising: the message to further indicate a link partner transmit waketime; and the second circuitry to determine a local receive wake timebased, at least in part, on the transmit wake value for the localphysical layer.
 44. The switch of claim 43, comprising: the secondcircuitry to determine the local receive wake time based on separatewake requirements of at least two power reduction modes.
 45. The switchof claim 44, comprising the separate wake requirements based on anetwork traffic load through the local physical layer.
 46. The switch ofclaim 45, comprising the network traffic load to cause a deeper powerreduction mode to be excluded from the at least two power reductionmodes.
 47. The switch of claim 44, comprising the separate wakerequirements based on thermal characteristics of a system that includesthe switch.
 48. The switch of claim 38, comprising the second circuitryto resolve to a longer transmit wake time based on a low bandwidthutilization rate to transmit data to the link partner compared to datathroughput capabilities.
 49. The switch of claim 38, further comprisingthe second circuitry to cause a message to be transmitted to the linkpartner, the message to include the local transmit wake time and thereceive wake time.
 50. The switch of claim 38, the message comprises alink layer discovery protocol frame.